Tomahawk49 wrote:

Jeredp wrote:Now let me ask this, whats the best way to measure your takeoff roll and climb performance while trying out these techniques? I was thinking about setting up my gopro on the ground, doing several takeoff, and then reviewing the footage.

I just did this last week testing out a bunch of short field techniques, my setup was an iPhone suctioned to the window recording video over the dash (could also see the airspeed and altitude gauge) along with an ipad recording my gps track with altitude info. At home I imported the gps tracks into google earth, which gave me a 3-d view of each takeoff profile. With this and the video footage and some deducing I was able to get a pretty good idea of how each technique worked.

What app did you use to get the 3d profile on your ipad?

Many GPS units have a glide ratio field available. Foreflight has a reasonable height above ground field available.

I've always had one result after playing with the glide ratio function to play with the best angle of climb configuration...any flaps whatsoever hurts the climb angle, at any altitude, and at any weight in the 182.

The penalty is slight until I get close to 10 degrees, but gets cut by over 1/4 at 20 degrees. At 30 degrees, the reduction is close to 50%.

My POH says to take off with 20 degrees and maintain until obstacles are cleared. It is fine for simplicity and focusing on the takeoff, but if I take off with 30 degrees of flap, I break ground faster, and if everything works out, getting the flaps up next to the ground until Vx always results in substantially more altitude over the 2000' mark of the runway. But it is a bit busy, and while I practice it, I only use it in the very few places I visit every year where takeoff performance is so important or the runway surface is too punishing.

lesuther wrote:My POH says to take off with 20 degrees and maintain until obstacles are cleared. It is fine for simplicity and focusing on the takeoff, but if I take off with 30 degrees of flap, I break ground faster, and if everything works out, getting the flaps up next to the ground until Vx always results in substantially more altitude over the 2000' mark of the runway. But it is a bit busy, and while I practice it, I only use it in the very few places I visit every year where takeoff performance is so important or the runway surface is too punishing.

Good example of the point I made earlier regarding POH recommendations on configurations. They have to write the POH for the person who is most likely to sue them if they botch the maneuver. Unfortunately.

MTV

Another thought, which I'm sure everyone who does these things is aware of but still needs to be said. Whenever you're doing something non-standard, i.e., not covered by the POH, you're in test pilot mode. If you really know your airplane well, that's not too bad. But if you're inexperienced with flying, period, or with flying that particular airplane, you're taking more risk than if you really know your airplane. Be realistic in assessing your skills. Over confidence can really lead to disaster.

A corollary is that some pilots have a better innate "feel" for what the airplane is doing than others. They are the ones who often are called "good stick & rudder" pilots--they seem to be one with the airplane. Others are extremely mechanical at what they do, so that anything out of the ordinary is not likely to come out well.

So be careful--as you said, no good reason to gamble with a $50K airplane for a $5 prize.

Cary

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Jeredp wrote:

Tomahawk49 wrote:

Jeredp wrote:Now let me ask this, whats the best way to measure your takeoff roll and climb performance while trying out these techniques? I was thinking about setting up my gopro on the ground, doing several takeoff, and then reviewing the footage.

I just did this last week testing out a bunch of short field techniques, my setup was an iPhone suctioned to the window recording video over the dash (could also see the airspeed and altitude gauge) along with an ipad recording my gps track with altitude info. At home I imported the gps tracks into google earth, which gave me a 3-d view of each takeoff profile. With this and the video footage and some deducing I was able to get a pretty good idea of how each technique worked.

What app did you use to get the 3d profile on your ipad?

Last week I used Foreflight's new track recording function, with the ipad linked to a Stratus external GPS receiver (I don't get very accurate results using just the built-in GPS receiver). GPS MotionX works too if not better. After some steps importing I end up with something looking like this in Google Earth, you're looking at my first two short field tests ... my plane is no Carbon Cub but the 2nd technique I used was clearly better for obstacle clearance:

Cary,

Excellent point, and again, if you're going to play these games, find an instructor who is intimately familiar with your aircraft type (Not some jackass who pronounces "No, I never flew one of these, but I've flown lots of planes, and they're all the same..." ). And try out some "performance" techniques.

Please, however, don't try this stuff without adult supervision.

MTV

Tomahawk 49,

When I first saw the Valdez short field takeoff and landing contest on this site, I was pleased that some were promoting good takeoff and landing techniques. I wondered, however, if there could be some way to reward following up this good get off the surface technique with good stay in low ground effect technique as long as practicable. Your google earth gps setup seem to make that possible.

It is not the extra ten degrees of flap that hurts your initial climb performance as much as pitching up and leaving low ground effect sooner than necessary. You mentioned your effort to reduce flaps while in low ground effect. After using good technique to get nose gear and then mains off as soon as possible and pitching level to stay in low ground effect and reducing flaps to a best climb position, it would be a shame to leave this great rapid acceleration position sooner than comfortably near the obstruction. Safety in not in how high we are at the 2,000' point, but in how much maneuverability we have at this point. By staying in low ground effect beyond Vx pressure airspeed and even to maximum pressure airspeed, we provide that much more kinetic energy to the wing at the critical point. It is so much more comforting, at least for an instructor, to go over the obstruction with a maneuverable airplane than to go over at the maximum altitude possible. So many times I have observed students and review pilots pull the airplane up through effective ground effect too fast and decelerate to the point, behind the power curve, that I had to convince them that they now had to push forward to go up.

That said, your shallower climb out, while not as impressive, was safer. More than just a few feet over the obstruction, the 2,000' point, is a waste of free kinetic energy that a C-177 can often make good use of.

Keep us posted on how things go.

Best regards,

Jim

MTV,

This question is for you.

I was practicing for the short take off contest last night and I am guessing that you have run into this before operating seaplanes.

With 35 degrees of flaps(approximately) the plane would get up on step and immediately begin to turn hard to the left even with full right rudder.

It doesn't do this nearly as bad with 20 degrees of flaps. I understand P-factor, but is it really this much worse just after getting on step with nearly full flaps?

Should I be going from 20 degrees to full flaps just prior to rotation to try to lessen this effect? (keep in mind the electric flaps are rather slow)

Also, have you quickly pushed the yoke forward to submerge more of the floats just before rotating? (Some people will call this dangerous I am sure)

-Levi

contactflying wrote:Safety in not in how high we are at the 2,000' point, but in how much maneuverability we have at this point. By staying in low ground effect beyond Vx pressure airspeed and even to maximum pressure airspeed, we provide that much more kinetic energy to the wing at the critical point.

Contact -- points well taken, use ground effect to build more airspeed which = energy which = more plane maneuverability over the obstacle and safety. I did try the method you're describing (here and in your book -- thanks again for that) as well, I understand the theory behind it, I do need to practice it more though. I wasn't able to hold the plane in ground effect for very long at all, she really wanted to climb out of it. I need to get the feel of it.

FWIW I felt the two tests depicted were safe, with the lower departure I was at Vx 77mph, the higher one at the POH recommended short-takeoff 69mph. I did full-power "departure stall" tests before this and the plane mushed in at around 52mph ... so I felt 69mph departure speed was plenty safe as far as stall margin and still had plenty of control.

contactflying wrote: So many times I have observed students and review pilots pull the airplane up through effective ground effect too fast and decelerate to the point, behind the power curve, that I had to convince them that they now had to push forward to go up.Jim

Excellent point, Jim. I have always told students "You don't have to clear the obstacle by 100 feet.....you just have to miss the obstacle". I'd much rather clear an obstacle by ten feet at Vy than clear it by 100 feet at Vx.....or slower

MTV

Levi wrote:MTV,

This question is for you.

I was practicing for the short take off contest last night and I am guessing that you have run into this before operating seaplanes.

With 35 degrees of flaps(approximately) the plane would get up on step and immediately begin to turn hard to the left even with full right rudder.

It doesn't do this nearly as bad with 20 degrees of flaps. I understand P-factor, but is it really this much worse just after getting on step with nearly full flaps?

Should I be going from 20 degrees to full flaps just prior to rotation to try to lessen this effect? (keep in mind the electric flaps are rather slow)

Also, have you quickly pushed the yoke forward to submerge more of the floats just before rotating? (Some people will call this dangerous I am sure)

-Levi

Levi,

Interesting. Only plane I ever met that would do that was a Beaver on 4580 floats, but even that plane was fine except in a slight left crosswind.

First: You said a C 172 with O 320, but what make and model floats? What model 172, ie: straight tail/swept tail, flat back/omni vision, ventral fin or not?

Second: Have you checked the float rigging PRECISELY? Send me a PM with a phone number if you don't know how to do this. It's not that hard.

Third: Do your flaps deploy symmetrically? As in, do they both deploy equally? A protracted can answer that question.

Fourth: Are your water rudders rigged absolutely straight aligned with the keels when in the UP position? No offense, but you are taking off with the rudders up, right?

I'll give this a bit more thought and if I think of anything else, I'll let you know.

I suspect that what's going on is that you're blanking out the rudder with that much flap deployed, and it may be that you'll just have to use a little less flap.....maybe.

In any case, verifying all the above will help your takeoff distance if any of this is off.

MTV

mtv wrote:

Levi wrote:MTV,

This question is for you.

I was practicing for the short take off contest last night and I am guessing that you have run into this before operating seaplanes.

With 35 degrees of flaps(approximately) the plane would get up on step and immediately begin to turn hard to the left even with full right rudder.

It doesn't do this nearly as bad with 20 degrees of flaps. I understand P-factor, but is it really this much worse just after getting on step with nearly full flaps?

Should I be going from 20 degrees to full flaps just prior to rotation to try to lessen this effect? (keep in mind the electric flaps are rather slow)

Also, have you quickly pushed the yoke forward to submerge more of the floats just before rotating? (Some people will call this dangerous I am sure)

-Levi

Levi,

Interesting. Only plane I ever met that would do that was a Beaver on 4580 floats, but even that plane was fine except in a slight left crosswind.

First: You said a C 172 with O 320, but what make and model floats? What model 172, ie: straight tail/swept tail, flat back/omni vision, ventral fin or not?

Second: Have you checked the float rigging PRECISELY? Send me a PM with a phone number if you don't know how to do this. It's not that hard.

Third: Do your flaps deploy symmetrically? As in, do they both deploy equally? A protracted can answer that question.

Fourth: Are your water rudders rigged absolutely straight aligned with the keels when in the UP position? No offense, but you are taking off with the rudders up, right?

I'll give this a bit more thought and if I think of anything else, I'll let you know.

I suspect that what's going on is that you're blanking out the rudder with that much flap deployed, and it may be that you'll just have to use a little less flap.....maybe.

In any case, verifying all the above will help your takeoff distance if any of this is off.

MTV

The other thing I would add is that engine torque is going to drive the left float into the water more at first - it doesn't take much for that water drag to have an effect on steering!

150HP c-172 POH says no flaps for short field, and 10' flaps for soft field. I do not know if this changes for later years with bigger motors.

The other thing I would add is that engine torque is going to drive the left float into the water more at first - it doesn't take much for that water drag to have an effect on steering![/quote]

I doubt that a O 320 is going to produce enough torque to create a noticeable effect in that regard. I've flown floatplanes with a lot more power and never encountered that sort of effect.....left turning tendency, yes, and control application to counter that will create drag and slow things down.

But....maybe, if the floats were mis-rigged??

MTV

Here's my 2 cents. Now this won't make much sense for a 172 with electric flaps but can still apply for Jared in his straight tail 172 with manual flaps. I fly a 170 with manual flaps so it's a lot easier to manipulate the flaps to your advantage on take off. What is the slowest speed the airplane will fly? Just above the full flap stall speed right? So that means once you reach this speed or just past it in your take off roll you can be flying if you do things right. My procedure for taking off as short as possible is to accelerate with the flaps up, get the tail up as soon as possible, and once I hit 40mph indicated airspeed I briskly rotate off the ground while yanking in full 40 degrees of flaps. This is basically pulling the plane straight into slow flight (I can fly slower than this with the sportsman wing, but the angle of attack is impossible to achieve in a taildragger on takeoff so I've found 40mph works good for me). Next I immediately start milking the flaps back to zero and lowering the nose to build airspeed then climb out at Vx, or Vy, whichever is more appropriate for the situation. I don't use this technique all the time but in my opinion it's best suited for short gravel bars or rough terrain when you need to be off the ground as soon as possible but are clear of obstacles once airborne to gain speed while milking the flaps back to zero. If you try doing this when obstacle clearance is an issue immediately after takeoff then the added drag from pulling in full flaps then milking them back to zero is going to hurt your acceleration and climb performance. For a situation like that just setting 20degrees of flaps, getting off the ground and into ground effect to build speed and reduce flaps to zero then climbing out at Vx will work better. In my experience my 170 always climbs better with zero flaps, so that's the configuration I try to get back to as soon as possible after takeoff.

Robw56,

The POH or published slowest stall speed was tested with the airplane OGE or out of ground effect. Any airplane will fly much slower than that published speed IGE or in ground effect. Not only that, the lower the height of the wheels IGE, the slower the airplane will fly.

On landing this slower than published stall speed is helpful. On takeoff we want to go as fast as possible before pitching up and burning the extra kinetic energy we have developed in low ground effect. However, we want to get off the wheels as soon as possible and into a level pitch attitude as low as possible. We want to fly the airplane off the surface as soon, as slow, as possible. Airplanes fly much better than they roll, especially in low ground effect.

We all have learned V speeds and terminology truisms that don't necessarily apply to the physics of the takeoff and landing situation. The aviation community didn't really get into serious ground effect considerations until helicopters became more common. Those IGE numbers have never been published, that I know of , for airplanes.

Sounds like you are making good application of these techniques, except for staying on the wheels too long.

Best regards,

Jim

I agree contact, the plane can fly slower. I'm already way below the published stall speed of 52mph... That's with a stock wing at gross weight though. Depending on weight it is hard to get the 170 off the ground much slower than 40mph. I can sometimes get off a little slower when very light. Try this at 35mph and it delays the takeoff a bit until I get a few more mph of airspeed.The angle of attack needed in my airplane to fly at this speed is just too high and the tailwheel prevents me from rotating enough to get airborne. Also ground effect isn't as effective in a high wing airplane, put it on bushwheels and the wings are even higher from the ground.

I see what you are saying, Rob. I have only been on the big wheels once, in a Maule, and I don't use the airspeed indicator. My 170 time was so long ago I don't remember what it flew like. With high winged airplanes it is very important to use the lowest wheel height we are comfortable with. Moving the stick fore/aft just a bit helps pin it there.

I use Contact's approach to departures in everything I fly, everytime I depart, unless noise abatement dictates otherwise... and even then I only deviate if it can be done reasonably safe..

I pretty much use Robs technique on every take off in almost everything I fly with one small deviation... and mastered, this deviation will help you find the sweet spot in any airplane faster and easier...

I honestly have no idea what speed any of our airplanes lift off at

The only time I have ever had the nerve to look at an ASI on take off was at an airport, or in an airplane that really wasn't made for backcountry stuff i.e. Baron, Seneca, etc.. What I do instead of waiting to nail an airspeed, is roll full aileron into the wind when I line up. Since I use the 'flap jump' or whatever you choose to call it, my flaps are retracted or set to an extension that will put the handle in a better position to extend. When the downwind wing tries to fly, it will fly with any further flap extension, and coincidentally so will the upwind wing .

This technique will cause a bunch of zig zag or herky jerky departures if you don't use it at least... almost all the time, so probably not a good idea if you don't care to practice it often. It also won't get you that last few inches of performance, if you are trying to win a contest. This is because you are reacting to a wing that's telling you it's been ready to fly. But, if you're looking for a repeatable way to safely depart short, this technique will work, and it will do so more consistently than just waiting for the tail to 'feel' right and then flapped or rotated, which if mistimed in either direction will cost yardage...

Take care, Rob

Since this thread is about take offs both land and sea, it's fair to say that there is a huge difference. Bear in mind that my expertise about seaplanes is pretty limited--8 hours and a SES doth not an expert make.

Comparing my airplane to the seaplane I trained in last month, the biggest difference was the density altitude. Both are older 172s; mine is a 63 P172D, the seaplane is a 64 172E. Both have Avcon conversions with 180hp Lycomings driving CS props. Mine has droopy tips and flap gap seals; the seaplane had neither.

With about the same load as the seaplane was carrying, i.e., full tanks, 2 people, and with 10 flaps, my airplane can easily leave the ground at a 6000' DA in less than 1000' and climb on out of ground effect at Vx if I want to. At a DA of probably 1650', the seaplane took easily 1500' of water run carrying 20 flaps before it would break free of the water, then milk up the flaps, let the speed build a bit and climb out at Vx, which was normal to leave Lake Union and clear all the buildings. If I lifted a float, it would break from the water a little sooner, but not a lot.

So comparing how to take off a seaplane with how to take off a land plane isn't really fair to either.

Cary